Aldehydes fragmentation mass

In the discussion of some mass spectra of nitrones (41), intermediate isomerization to oxaziridines was concluded from the occurrence of aldehyde fragments. 

Attack of the OH radical on carbohydrates of low molecular mass gives rise to a variety of products. Indeed, the reaction of radiolytically-generated OH radical with lower hexose sugars produces lower saccharides (for di- and higher saccharide species), uronic and aldonic acids, and 3-, 2- and 1-carbon aldehydic fragments, e.g. 

All hydrazones show a significant absorption band due to the C —N double bond at 1600-1645 cm-1 for ketone hydrazones, and at 1600-1610 cm"1 for the aldehyde derivatives. Mass spectra are characterized by a typical fragmentation pattern and a base peak corresponding to the methoxymethyl fragment6. 

McLafferty Rearrangement of Ketones and Aldehydes The mass spectrum of butyraldehyde (Figure 18-4) shows the peaks we expect at m/z 72 (molecular ion), m/z 57 (loss of a methyl group), and m/z 29 (loss of a propyl group). The peak at m/z 57 is from cleavage between the /3 and y carbons to give a resonance-stabilized carbocation. This is also a common fragmentation with carbonyl compounds like the other odd-numbered peaks, it results from loss of a radical. 

Mass Spectrometry Aldehydes and ketones typically give a prominent molecular ion peak m their mass spectra Aldehydes also exhibit an M— 1 peak A major fragmentation pathway for both aldehydes and ketones leads to formation of acyl cations (acylium ions) by cleavage of an alkyl group from the carbonyl The most intense peak m the mass spectrum of diethyl ketone for example is m z 57 corresponding to loss of ethyl radi cal from the molecular ion... 

An example of how information from fragmentation patterns can be used to solve structural problems is given in Worked Example 12.1. This example is a simple one, but the principles used are broadly applicable for organic structure determination by mass spectrometry. We ll see in the next section and in later chapters that specific functional groups, such as alcohols, ketones, aldehydes, and amines, show specific kinds of mass spectral fragmentations that can be interpreted to provide structural information. 

TABLE 5.2. IE of the Complementary Fragments and the Intensities of the Corresponding Peaks in the Mass Spectra of Aldehydes... 

Fig. 11.4. Electron ionization mass spectrum of nonanal. Unlike the previous example (toluene, Fig. 11.3), this 9-carbon alkyl aldehyde displays extensive fragmentation and a very low abundance molecular ion at mlz 142. The extensive degree of fragmentation exhibited by many compounds under El conditions makes manual interpretation complex and tedious. Consequently, computerized searches of spectral libraries find extensive use in compound identification.

Fig. 2.9.15. APCI-FIA-MS-MSMS-MS(+) (CID) product ion mass spectrum of selected [M + NH4]+ parent ion (m/z 266) compound was identified as metabolite (aldehyde compound) of degradation product of non-ionic surfactant compound PPG (general formula H0-(CH(CH3)-CH2-0)x-CH(CH3)-CH0 ( = 3) fragmentation behaviour under CID presented in the inset [22].

Liedtke, R.J. Djerassi, C. Mass Spectrometry in Structural and Stereochemical Problems. CLXXXIII. A Study of the Electron Impact Induced Fragmentation of Aliphatic Aldehydes. J. Am. Chem. Soc. 1969,97,6814-6821. 

Identification. Identification of the carbonyl PFBOA derivatives was performed by mass spectrometry using electron impact ionization running in the scan mode. It was confirmed that fragment m/z 181 was the main fragment of all analyzed aldehydes (6). Figure 1 shows as an example the mass spectrum of the PFBOA derivative of methi-onal. To increase the selectivity of the method, all aldehyde analyses were run in the... 

Comparison of the HREI-MS of N-formylstaurosporine (309) with (+)-stauro-sporine (295) (see Scheme 2.74) indicated the presence of an additional carbonyl group. The EI-MS spectrum mass fragmentation ion at m/z 466 (M -CO) indicated the presence of a formyl group. Additionally, the presence of an aldehyde functionality was confirmed by the characteristic IR bands at v ax 1670 (C = 0), 2840 (aldehyde CH) cm The and C-NMR spectra of N-formylstaurosporine... 

Examples of aldehydes used to obtain the respective heterocycles are mentioned directly in the text. This work. KIP values are Kovdts indices on a polar column (FFAP) the values in parentheses are estimates based on additivity of index increments. Base peak and main fragments. Unless indicated otherwise, the mass spectra were obtained in this work and are in agreement with the literature data (see the ref.). %ot reported. Literature data. First isomer. Second isomer. Found by Ledl (33) after the reaction of acetaldehyde with hydrogen sulfide. 

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